A distributed antenna system (DAS) receives signals transmitted from a base station to remove shadow areas that necessarily occur indoors or outdoors and to increase the capacity of data. Generally, the DAS performs a function of receiving a downlink signal transmitted from a base station and re-transmitting, to the base station, an uplink signal transmitted from a subscriber terminal in a corresponding service area.
Therefore, signal matching between a base station (i.e., a base transceiver system (BTS)) and the DAS is required. That is, a base station signal (a BTS signal) is matched in a duplexer type where Tx and Rx are coupled, and a DAS signal is generally configured in a simplexer type where Tx and Rx are separated. Therefore, a signal matching device for matching between the base station signal and the DAS signal is required. The signal matching device is configured as a separate device (i.e., an external BTS signal matching device) at an outside of the DAS (see FIG. 1).
In this state, the external BTS signal matching device uses an attenuator for attenuating the output of a signal from a base station to switch a signal of a high power level from the base station to an appropriated level of a signal from the DAS, and a filter for separating a base station signal of the duplexer type, transmitted from the BTS, into downlink and uplink signals.
In a conventional art, passive elements in the external BTS signal matching device should deal with high output power of the base station. Therefore, in the conventional art, a high power attenuator and a cavity filter are used as the passive elements as shown in FIG. 2. In this case, the passive elements are very high priced, and the size of the device is also increased. Here, the cavity filter has a form in which Tx and Rx signals are coupled, and performs a function of separating a signal input through one port into Tx and Rx signals of the input signal.
In the conventional art, a high power attenuator is used as the attenuator in order to deal with a high output of the base station, and therefore, the passive intermodulation (PIM) characteristic of the attenuator is not good. Accordingly, as a method for solving this problem in the conventional art, the components are arranged in the order of the cavity filter→the high power attenuator, thereby reducing the PIM characteristic. However, two high power attenuators are required rather than one high power attenuator according to the arrangement order described above. In FIG. 2, the external BTS signal matching device is separately provided with an attenuator for performing signal attenuation at a power level suitable for inputting a high power signal in a Tx signal direction (i.e., a downlink direction) to the DAS, and an attenuator for performing signal attenuation at a power level necessary for transmitting a DAS signal (i.e., a terminal signal processed by the DAS) in an Rx signal direction (i.e., an uplink direction) to the base station (BTS). In the conventional art, two high power attenuators are required as described above, and therefore, the cost of the device increases.
In addition, the external signal matching device is configured with passive elements, and hence input/output signal level (power level) and the like cannot be monitored.
An embodiment of the inventive concept is directed to a relay device in which a base station signal matching device for matching a base station signal transmitted from a base transceiver system (BTS) is embedded in a donor equipment in a relay system such as a distributed antenna system, so that it is unnecessary to dispose a separate BTS matching device at an outside of the relay device for the purpose of base station signal matching.
Another embodiment of the inventive concept is directed to a base station signal matching device which can improve passive intermodulation characteristics, reduce the entire manufacturing cost and volume of a product, and perform power monitoring of Tx/Rx signals.